Process for etching photomasks

ABSTRACT

Method and apparatus for etching a metal layer disposed on a substrate, such as a photolithographic reticle, are provided. In one aspect, a method is provided for processing a substrate including positioning a substrate having a metal photomask layer disposed on a silicon-based material in a processing chamber, introducing a processing gas at a flow rate of greater than about 350 sccm with the processing gas comprising an oxygen containing gas, a halogen containing gas, and optionally, an inert gas, into the processing chamber, generating a plasma of the processing gas in the processing chamber, generating a bias of about 50 watts or less, and etching exposed portions of the metal layer disposed on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional patentapplication serial No. 60/374,239, filed Apr. 19, 2002, which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the fabrication of integratedcircuits and to the fabrication of photolithographic reticles useful inthe manufacture of integrated circuits.

[0004] 2. Background of the Related Art

[0005] Semiconductor device geometries have dramatically decreased insize since such devices were first introduced several decades ago. Sincethen, integrated circuits have generally followed the two year/half-sizerule (often called Moore's Law), which means that the number of deviceson a chip doubles every two years. Today's fabrication plants areroutinely producing devices having 0.15 μm and even 0.13 μm featuresizes, and tomorrow's plants soon will be producing devices having evensmaller geometries.

[0006] The increasing circuit densities have placed additional demandson processes used to fabricate semiconductor devices. For example, ascircuit densities increase, the widths of vias, contacts and otherfeatures, as well as the dielectric materials between them, decrease tosub-micron dimensions, whereas the thickness of the dielectric layersremains substantially constant, with the result that the aspect ratiosfor the features, i.e., their height divided by width, increases.Reliable formation of high aspect ratio features is important to thesuccess of sub-micron technology and to the continued effort to increasecircuit density and quality of individual substrates.

[0007] High aspect ratio features are conventionally formed bypatterning a surface of a substrate to define the dimensions of thefeatures and then etching the substrate to remove material and definethe features. To form high aspect ratio features with a desired ratio ofheight to width, the dimensions of the features are required to beformed within certain parameters that are typically defined as thecritical dimensions of the features. Consequently, reliable formation ofhigh aspect ratio features with desired critical dimensions requiresprecise patterning and subsequent etching of the substrate.

[0008] Photolithography is a technique used to form precise patterns onthe substrate surface, and then the patterned substrate surface isetched to form the desired device or features. Photolithographytechniques use light patterns and resist materials deposited on asubstrate surface to develop precise patterns on the substrate surfaceprior to the etching process. In conventional photolithographicprocesses, a resist is applied on the layer to be etched, and thefeatures to be etched in the layer, such as contacts, vias, orinterconnects, are defined by exposing the resist to a pattern of lightthrough a photolithographic reticle having a photomask layer disposedthereon. The photomask layer corresponds to the desired configuration offeatures. A light source emitting ultraviolet (UV) light or low X-raylight, for example, may be used to expose the resist in order to alterthe composition of the resist. Generally, the exposed resist material isremoved by a chemical process to expose the underlying substratematerial. The exposed underlying substrate material is then etched toform the features in the substrate surface while the retained resistmaterial remains as a protective coating for the unexposed underlyingsubstrate material.

[0009] Photolithographic reticles typically include a substrate made ofan optically transparent silicon-based material, such as quartz (i.e.,silicon dioxide, SiO₂), having an opaque light-shielding layer of metal,or photomask, typically chromium, disposed on the surface of thesubstrate. The light-shielding layer is patterned to correspond to thefeatures to be transferred to the substrate. Generally, conventionalphotolithographic reticles are fabricated by first depositing a thinmetal layer on a substrate comprising an optically transparentsilicon-based material, such as quartz, and depositing a resist layer onthe thin metal layer. The resist is then patterned using conventionallaser or electron beam patterning equipment to define the criticaldimensions to be transferred to the metal layer. The metal layer is thenetched to remove the metal material not protected by the patternedresist; thereby exposing the underlying silicon-based material andforming a patterned photomask layer. Photomask layers allow light topass therethrough in a precise pattern onto the substrate surface.

[0010] Conventional etching processes, such as wet etching, tend to etchisotropically, which can result in an undercut phenomenon to occur inthe metal layer below the patterned resist. The undercut phenomenon canproduce patterned features on the photomask that are not uniformlyspaced nor do the features have desired straight, vertical sidewalls,thereby losing the critical dimensions of the features. Additionally,the isotropic etching of the features may overetch the sidewalls offeatures in high aspect ratios, resulting in the loss of the criticaldimensions of the features. Features formed without the desired criticaldimensions in the metal layer can detrimentally affect light passingtherethrough and result in less than desirable patterning by thephotomask in subsequent photolithographic processes.

[0011] Plasma etch processing, known as dry etch processing or dryetching, provides an alternative to wet etching and a more anisotropicetch than wet etching processes. The dry etching process has been shownto produce less undercutting and to improve the retention of thecritical dimensions of the photomask features with straighter sidewallsand flatter bottoms. In conventional dry etching processing, a plasma ofetching gases, such as chlorine, oxidizing gases, such as oxygen, andinert gases, such as helium, are used to etch the metal layers formed onthe substrate. The etching gases are introduced into the processingsystems at flow rates of less than 300 sccm for etching conventionalphotomask reticles.

[0012] Oxidizing gases, such as oxygen, promote overetching or impreciseetching of the sidewalls of the openings formed in the resist materialused to define the critical dimensions of the metal layer. Excess sideremoval of the resist material results in a loss of the criticaldimensions of the patterned resist features, which may correspond to aloss of critical dimensions of the features formed in the metal layerdefined by the patterned resist layer. It has been observed thatincreasing flow rates of etching gases causes excessive etching of bothresist materials and substrate materials.

[0013] One solution to excessive etching is to minimize the amount ofetching gases or to reduce the concentration of etching gases in theplasma being generated for dry etch processing. However, suchcompositions have been observed not to sufficiently etch the features toprovide the necessary critical dimensions. Failure to sufficiently etchthe features to the critical dimensions is referred to as a “gain” ofcritical dimensions. The degree of loss or gain of the criticaldimensions in the metal layer is referred to as “etching bias” or “CDbias”. The etching bias can be as large as 120 nm in photomask patternsused to form 0.14 μm features on substrate surfaces.

[0014] The loss or gain of critical dimensions of the pattern formed inthe metal layer can detrimentally affect the light passing therethroughand produce numerous patterning defects and subsequent etching defectsin the substrate patterned by the photolithographic reticle. The loss orgain of critical dimensions of the photomask can result in insufficientphotolithographic performance for etching high aspect ratios ofsub-micron features, and if the loss or gain of critical dimensions issevere enough, the failure of the photolithographic reticle orsubsequently etched device.

[0015] One solution to preserving the critical dimensions of a featureis to use processing gases containing passivating materials, such ashydrocarbons, which may form polymeric deposits on the sidewalls offeatures and prevent overetching. However, polymer-forming compounds maydeposit on chamber components and become a source of particulate matterin the processing chamber. Particulate matter may deposit on thesubstrate surface and detrimentally affect the etching process as wellas subsequent processing.

[0016] Therefore, there remains a need for a process and chemistry foretching a metal layer on a substrate, such as a reticle, to produce apattern with desired critical dimensions in the metal layer.

SUMMARY OF THE INVENTION

[0017] Aspects of the invention generally provide methods and relatedchemistry for etching a metal layer deposited on a silicon-basedsubstrate, such as a photolithographic reticle. In one aspect, a methodis provided for processing a photolithographic reticle includingpositioning the reticle on a support member in a processing chamber,wherein the reticle comprises a metal photomask layer formed on asilicon-based substrate and a patterned resist material deposited on themetal photomask layer, introducing a processing gas at a flow rate ofgreater than about 300 sccm, wherein the processing gas comprises anoxygen containing gas and a halogen containing gas, and delivering powerto the processing chamber to generate a plasma of the processing gas,and supplying a bias power to the support member of greater than about 5watts, and removing exposed portions of the metal photomask layer.

[0018] In another aspect, a method is provided for processing aphotolithographic reticle including positioning the reticle on a supportmember in a processing chamber, wherein the reticle comprises achromium-based photomask layer formed on an optically transparentsilicon-based material and a patterned resist material deposited on thechromium-based photomask layer, introducing a processing gas comprisingchlorine gas and oxygen gas at a flow rate of at least 350 sccm, whereinthe molar ratio between the chlorine gas and the oxygen gas is betweenabout 1:1.5 and about 4:1, maintaining a chamber pressure between about2 milliTorr and about 50 milliTorr, delivering power to the processingchamber of about 1000 watts or less to a coil disposed in the processingchamber to generate a plasma, supplying a bias power to the supportmember of greater than about 5 watts, and etching exposed portions ofthe chromium-based photomask layer and removing the chromium-basedphotomask layer at a removal rate ratio of chromium-based photomasklayer to resist material of about 1:1 or greater.

[0019] In yet another aspect, a method is provided for processing areticle including positioning the reticle on a support member in aprocessing chamber, wherein the reticle comprises a chromium-basedphotomask layer formed on an optically transparent silicon-basedmaterial and a patterned resist material deposited on the chromium-basedphotomask layer, introducing a first processing gas comprising an inertgas, a halogen containing gas, and an oxygen containing gas, wherein thehalogen containing gas and the oxygen containing gas have a flow rate ofabout 100 sccm or less, delivering power to the processing chamber ofabout 1000 watts or less to a coil disposed in the processing chamber togenerate a plasma, introducing a second processing gas comprising ahalogen containing gas, and an oxygen containing gas, wherein thehalogen containing gas and the oxygen containing gas have a flow rate ofat least 350 sccm, delivering power to the processing chamber of about1000 watts or less to a coil disposed in the processing chamber tomaintain a plasma, supplying a bias power to the support member ofgreater than about 5 Watts, and etching exposed portions of thechromium-based photomask layer

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] So that the manner in which the above recited aspects of theinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

[0021] It is to be noted, however, that the appended drawings illustrateonly typical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

[0022]FIG. 1 is a schematic cross-sectional view of one embodiment of anetching chamber;

[0023]FIG. 2 is a flow chart illustrating one embodiment of a sequencefor processing a substrate according to one embodiment of the invention;

[0024] FIGS. 3A-3E are cross-sectional views showing an etching sequenceof another embodiment of the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0025] Aspects of the invention will be described below in reference toan inductively coupled plasma etch chamber. Suitable inductively coupledplasma etch chambers include the Decoupled Plasma Source (DPS™) chamberavailable from Applied Materials, Inc., of Santa Clara, Calif., or theETEC Tetra™ photomask etch chamber available from ETEC of Hayward,Calif.

[0026] Other process chambers may be used including, for example,capacitively coupled parallel plate chambers and magnetically enhancedion etch chambers, as well as inductively coupled plasma etch chambersof different designs. Examples of such suitable processing chambers aredisclosed in U.S. patent application Ser. No. 09/325,026, filed on Jun.3, 1999, which is incorporated by reference to the extent notinconsistent with the claims and disclosures described herein. Althoughthe processes are advantageously performed with the DPS™ processingchamber, the description in conjunction with the DPS™ processing chamberis illustrative and should not be construed or interpreted to limit thescope of aspects of the invention.

[0027]FIG. 1 is a schematic cross-sectional view of one embodiment of aDPS™ processing chamber that may be used for performing the processesdescribed herein. The processing chamber 10 generally includes acylindrical sidewall or chamber body 12, an energy transparent dome 13mounted on the body 12, and a chamber bottom 17. A flat lid (not shown)or other alternative lid capable of being used with an inductive coilmay be used in place of the dome 13. An inductive coil 26 is disposedaround at least a portion of the dome 13. The chamber body 12 and thechamber bottom 17 of the processing chamber 10 can be made of a metal,such as anodized aluminum, and the dome 13 can be made of an energytransparent material such as a ceramic or other dielectric material.

[0028] A substrate support member 16 is disposed in the processingchamber 10 to support a substrate 20 during processing. The supportmember 16 may be a conventional mechanical or electrostatic chuck withat least a portion of the support member 16 being electricallyconductive and capable of serving as a process bias cathode. While notshown, a reticle adapter may be used to secure the reticle on thesupport member 16. The reticle adapter generally includes a lowerportion milled to cover an upper portion of the support member and a topportion having an opening that is sized and shaped to hold a reticle. Asuitable reticle adapter is disclosed in U.S. Pat. No. 6,251,217, issuedon Jun. 26, 2001, which is incorporated herein by reference to theextent not inconsistent with aspects and claims of the invention.

[0029] Processing gases are introduced into the processing chamber 10from a process gas source (not shown) through a gas distributor 22peripherally disposed about the support member 16. Mass flow controllers(not shown) for each processing gas, or alternatively, for mixtures ofthe processing gas, are disposed between the processing chamber 10 andthe process gas source to regulate the respective flow rates of theprocess gases. The mass flow controllers can regulate up to about 1000sccm flow rate for each processing gas or processing gas mixture.

[0030] A plasma zone 14 is defined by the process chamber 10, thesubstrate support member 16 and the dome 13. A plasma is formed in theplasma zone 14 from the processing gases using a coil power supply 27 topower the inductor coil 26 to generate an electromagnetic field in theplasma zone 14. The support member 16 includes an electrode disposedtherein, which is powered by an electrode power supply 28 and generatesa capacitive electric field in the processing chamber 10. Typically, RFpower is applied to the electrode in the support member 16 while thebody 12 is electrically grounded. The capacitive electric field istransverse to the plane of the support member 16, and influences thedirectionality of charged species to provide more vertically orientedanisotropic etching of the substrate 20.

[0031] Process gases and etchant byproducts are exhausted from theprocess chamber 10 through an exhaust system 30. The exhaust system 30may be disposed in the bottom 17 of the processing chamber 10 or may bedisposed in the body 12 of the processing chamber 10 for removal ofprocessing gases. A throttle valve 32 is provided in an exhaust port 34for controlling the pressure in the processing chamber 10. An opticalendpoint measurement device can be connected to the processing chamber10 to determine the endpoint of a process performed in the chamber.

[0032] While the following process description illustrates oneembodiment of etching a substrate using processing gases as describedherein, the invention contemplates the use of processing parametersoutside the ranges described herein for performing this process indifferent apparatus, such as a different etching chamber, and fordifferent substrate sizes, such as photolithographic reticles for 300 mmsubstrate processing.

[0033] Exemplary Etch Process

[0034] Generally a photolithographic reticle includes a metal layer,such as chromium or chromium oxynitride, known as a photomask, depositedon an optically transparent substrate. The metal layer is etched toproduce a photomask layer having features with desired criticaldimensions. A processing gas including an oxygen containing gas and ahalogen containing gas is used for etching the metal layer. Theprocessing gas may include an inert gas. The processing gas has a flowrate greater than about 300 sccm. Etching of exposed metal materialoccurs by generating a plasma of the processing gas and supplying a biasto the reticle of greater than about 5 watts. A plasma strike may beused to initiate or generate the plasma prior to introducing theprocessing gas at the compositions and flow rates described herein forthe etching process. The etching process described herein surprisinglyand unexpectedly etched exposed metal layers with minimal etch bias,vertical etch profiles, and produced openings and patterns havingdesired critical dimensions.

[0035] The processing gas may include an oxygen containing gas and ahalogen containing gas. The oxygen containing gas may include oxygen(O₂), carbon monoxide (CO), carbon dioxide (CO₂), and combinationsthereof, of which oxygen is preferred. The oxygen containing gasprovides a source of etching radicals. Carbon containing, oxygencontaining gases may provide a source of material for passivatingpolymer deposits which may improve etch bias.

[0036] The halogen containing gas may include chlorine containing gasesselected from the group of chlorine (Cl₂), carbon tetrachloride (CCl₄),hydrochloric acid (HCl), and combinations thereof, of which Cl₂ ispreferred, which are used to supply highly reactive radicals to etch themetal layer. The chlorine containing gas provides a source of etchingradicals and Carbon containing chlorine containing gases may provide asource of material for forming passivating polymer deposits that mayimprove etch bias.

[0037] The halogen containing gas and the oxygen containing gas areprovided in a molar ratio of halogen containing gas and the oxygencontaining gas of between about 1:1.5 and about 4:1, for example, achlorine to oxygen molar ratio of about 2.7:1. The molar ratiotranslates into the halogen containing gas generally including betweenabout 40% and about 80% of the total moles of the processing gas. Aconcentration of halogen containing gas of between about 50 vol % andabout 70 vol % has been observed to provide satisfactory etchingresults.

[0038] The processing gas may also include an inert gas which, whenionized as part of the plasma including the processing gas, results insputtering species to increase the etching rate of the features. Thepresence of an inert gas as part of the plasma may also enhancedissociation of the active processing gases. Examples of inert gasesinclude argon (Ar), helium (He), neon (Ne), xenon (Xe), krypton (Kr),and combinations thereof, of which argon and helium are generally used.The inert gas may be provided in a molar ratio of oxygen containing gasto inert gas of between about 0.5:1 and about 1:1, for example a heliumto oxygen molar ratio of about 0.7:1. The inert gases typically comprisebetween about 5 vol % and about 40 vol %, such as between about 15 vol %and about 25 vol % of the total gas flow for the process. A “striking”gas of between about 75 vol % and about 100 vol % of an inert gas may beused to initiate the plasma prior to introducing the etching processinggas.

[0039] The total flow rate of the processing gases, including the inertgases, are introduced at a flow rate of greater than about 300 sccm,such as between about 300 sccm and about 1000 sccm for etching a 150 mmby 150 mm square photolithographic reticle in an etch chamber. A totalprocessing gas flow rate between about 400 sccm and about 700 sccm maybe used in the etching process described herein. However, the total gasflow of the processing gas, including the inert gas flow, may vary basedupon a number of processing factors, such as the size of the processingchamber, the size of the substrate being processed, and the specificetching profile desired by the operator.

[0040] The halogen containing gas is introduced into the processingchamber at a flow rate of at least about 200 sccm for etching a 150 mmby 150 mm square photolithographic reticle in an etch chamber. Thehalogen containing gas may have a flow rate between about 200 sccm andabout 600 sccm for use in the etching process described herein.

[0041] The oxygen containing gases are introduced into the processingchamber at a flow rate of at least 100 sccm for etching a 150 mm by 150mm square photolithographic reticle in an etch chamber. Typically, theoxygen containing gas has a flow rate of at least 150 sccm, such asbetween about 150 sccm and about 400 sccm, for use in the etchingprocess described herein.

[0042] Generally, the processing chamber pressure is maintained betweenabout 2 milliTorr and about 50 milliTorr. A chamber pressure betweenabout 5 milliTorr and about 35 milliTorr, preferably between about 15milliTorr and about 32 milliTorr may be maintained during the etchingprocess.

[0043] The substrate temperature during processing is about 150° C. orless. A substrate temperature below about 150° C. or less has minimalheat degradation of materials, such as resist materials, deposited onthe substrate during the photolithographic reticle fabrication processeswith the processing gases described herein. The substrate temperaturebetween about 20° C. and about 150° C., preferably between about 20° C.and about 50° C., may be used to etch photomask features with minimalheat degradation of material disposed on the substrate surface. It isalso believed that the substrate temperature helps regulate theformation of passivating polymer deposits by limiting polymerizationreactions during the etching process. Additionally, the sidewalls of theprocessing chamber are maintained at a temperature of less than about70° C., and the dome is maintained at a temperature of less than about80° C. to maintain consistent processing conditions and to minimizepolymer formation on the surfaces of the processing chamber.

[0044] Generally, a source RF power level of about 1000 watts or less isapplied to an inductor coil to generate and sustain a plasma of theprocessing gases during the etching process. A power level between about300 watts and about 1000 watts, such as about 650 watts, has beenobserved to provide sufficient plasma of the processing gases foretching the substrate surface. The recited source RF power levels havebeen observed to produce sufficient etching radicals and polymerizationradicals from the processing gases to etch the exposed metal layerdisposed on the substrate while providing a sufficiently low powerlevel, compared to prior art metal etch processes, for the substratetemperatures to be about 150° C. or less.

[0045] Generally, a bias power of less than about 200 watts is appliedto the substrate to increase directionality of the etching radicals withrespect to the surface of the substrate. A bias power of less than 50watts, such as between about 20 watts and about 40 watts, may be used inthe etching process. A bias between about 25 watts and 35 watts has beenobserved to provide sufficient directionality of etching radicals duringthe etching process.

[0046] It has been surprisingly and unexpectedly observed that theprocessing gas flow rates of greater than about 300 sccm and an appliedbias power greater than about 5 watts, for example, between about 20watts and 40 watts, etch metal layers with vertical etch profiles, andproduce openings and patterns having desired critical dimensionscompared to prior art etching process having lower flow rate of lessthan 300 sccm or less and low bias powers of about 5 watts or less. Itwas also surprising and unexpected to produce such results in theabsence of passivating gases as used in prior art applications.

[0047] The etching processes described herein, under the conditionsdisclosed, produces a removal rate ratio, i.e., selectivity or etchbias, of metal layer to resist of about 1:1 or greater. A selectivity ofchromium to resist of about 3:1 or greater has been observed insubstrates processed by the etching process described herein. Increasedselectivity results in preserving the critical dimension patterned inthe photoresist layer and allows for etched chromium features to havethe desired critical dimensions. The etching process was also observedto remove “top” or upper surface resist material independent of “side”feature resist material, which is consistent with anisotropic etchingand improved feature formation. Additionally, processed substrates haveproduced features with the desired critical dimension with an almostvertical profile, i.e., an angle of about 90° between the sidewall ofthe feature and the bottom of the feature compared to prior art resultsof about 85° to about 88°.

[0048] It has also been observed that etching the metal layers of thereticles have improved micro-loading, macro-loading, and linearity, overprior art etch processes having lower flow rates and lower bias powersthan described herein. Micro-loading is broadly defined herein as thedifference in the etch rates of the same material disposed in or exposedby different sized feature definitions, i.e., the difference in etchingrates of the same material exposed by a 1 μm width feature and a 100 μmwidth feature. Improved micro-loading is broadly understood as havingsimilar etching rates for different sized features. Macro-loading isbroadly defined herein as the difference in the etch rates of differentamounts of exposed materials, i.e., the difference in etching rates fora substrate surface exposing 1% chromium or 90% chromium. Improvedmacro-loading is broadly understood as having similar etching rates fordifferent amounts of exposed materials. Linearity is broadly definedherein as the difference between the actual features etched and thedesired or patterned feature for a number of different sized features,i.e., the difference in the actual size of 0.24 micron and 1 micronsized features from the resist pattern of 0.24 micron and 1 micron sizedfeatures. Improved linearity is broadly understood as having improvedaccuracy and reproducibility of the features from the patterned resist.

[0049] It is believed that generating a plasma of the processing gasesat increased processing gas flow rates and increased bias power removesexposed portions of the metal layer without excessive etching of thesidewalls of the openings (or pattern) formed in the resist material andthose features being formed in the metal layer during etching to producethe desired critical dimensions.

[0050] In one aspect, a plasma strike may be used to generate the plasmain the processing chamber prior to introducing the processing gases forthe etching process at the desired amounts and concentrations asdescribed herein. It is believed that helium atoms are more likely toionize greater and form a more uniform plasma under processingconditions having equivalent power levels than chlorine atoms or oxygenatoms. The ionization of helium allows for a plasma to be generated athigher chamber pressures and at lower source power and higher bias poweras well as forming a stable plasma more rapidly than halogen containinggases and oxygen containing gases.

[0051] A processing gas for the plasma strike generally includes aninert gas, optionally, an oxygen containing gas as described herein, oroptionally, a halogen containing gas as described herein. The plasmastrike processing gas is introduced into a processing chamber at betweenabout 300 sccm and about 1000 sccm, for example, a flow rate of about500 sccm. When the oxygen containing gas and the halogen containing gasare present in the plasma strike processing gas, the flow rates of thecombined gases are about 100 sccm or less of the total flow rate. Theoxygen containing gas may have a flow rate of about 100 sccm or less,and the halogen containing gas may have a flow rate of about 100 sccm orless. A molar ratio of halogen containing gas to oxygen containing isgenerally about 1:1 or greater, such as a chlorine to oxygen molar ratioof about 1.33:1. A molar ratio of inert gas to oxygen containing gas isgenerally about 3:1 or greater, such as a helium to oxygen molar ratioof about 5:1. The gas flow rates may be introduced into the processingchamber for less than 30 seconds, such as about 5 seconds, forstabilization of the processing gas flow rates.

[0052] The chamber pressure is established between about 2 milliTorr andabout 50 milliTorr, for example, between about 20 milliTorr and about 30milliTorr. Source power is supplied to a coil at a range between about300 watts and about 1000 watts, such as about 500 watts. A bias issupplied at a range between about 1 watt and about 50 watts, such asbetween about 20 watts and about 40 watts. The source power used tostrike the plasma may be less than the power used during etching of thesubstrate. The processing conditions and the plasma conditions of theplasma strike process may approximate those of the etching process withthe processing gas described herein including total flow rates, chamberpressures, source power, and bias power. The plasma strike process maybe for about 15 seconds or less, such as between about 1 and about 5seconds.

[0053] An example of a plasma strike process is as follows. A plasmastrike processing gas, comprising helium, chlorine, and oxygen, isintroduced into the processing chamber at a total flow rate of about 480sccm with a helium flow rate of about 400 sccm, a chlorine flow rate ofabout 50 sccm, and an oxygen flow rate of about 30 sccm for a period ofabout 5 seconds. The chamber pressure is established at about 20milliTorr, and a plasma strike is generated by applying a source powerof 500 watts with an applied bias power of 30 watts for about 3 seconds.

[0054] The processing of the substrate may include a power applicationprocess of striking a plasma, modifying the power level to that of theetching conditions, for example, striking a plasma at 500 watts butetching at 650 watts, stabilizing the power, and then performing theetch process. The power application process may be performed for a fewseconds in which etching of the substrate surface may occur. However,adjusting the flow rates of the reactive oxygen containing and halogencontaining processing gas to less than 100 sccm minimizes etching.Etching is also minimized by utilizing a source power level that islower than that of the subsequent etching step. After striking theplasma, the processing gas composition may be modified to that of theetching gas by reducing the inert gas flow rate and increasing the flowrate of the halogen containing gas and the oxygen containing gas.

[0055] While the following description illustrates one embodiment of aprocess sequence for etching metal layers, such as chromium and chromiumoxynitride, as photomasks in photolithographic reticle fabrication, itis contemplated that the etching gases may be used to etch other metallayers formed on substrates in semiconductor and photolithographicreticle manufacturing.

[0056]FIG. 2 is a flow chart of one embodiment of one sequence of anetching process. The flow chart is provided for illustrative purposesand should not be construed as limiting the scope of the aspects of theinvention. A substrate, typically comprising a silicon-based reticle,such as optical quality quartz, molybdenum silicide, or molybdenumsilicon oxynitride (MoSi_(X)N_(Y)O_(Z)) is provided to a processingchamber at step 210, such as the DPS™ processing chamber 10 of FIG. 1.The substrate is then processed by depositing an opaque metal layer as ametal photomask layer, typically comprising chromium, on the substrateat step 220.

[0057] The dimensions of openings or patterns to be formed in the metallayer are patterned by depositing and pattern etching a first resistmaterial to expose the metal photomask layer at step 230. The resistmaterials used in photolithographic reticle fabrication are usually lowtemperature resist materials, defined herein as materials that thermallydegrade at temperatures above about 250° C. Resist materials may bepatterned optically, i.e., photoresist materials, or by anotherradiative energy patterning device, such as an ion beam emitter.Openings and patterns are then formed by etching the metal photomasklayer to expose the underlying substrate at step 240 using processinggas containing the oxygen containing gas and halogen containing gas at aflow rate of greater than about 300 sccm and an applied bias of greaterthan about 5 watts. Optionally, a plasma strike may be used to generatethe plasma for etching the metal photomask layer. Following the etchingstep, any remaining resist materials are removed.

[0058] Optionally, the substrate may then be further processed to etchthe silicon-based materials for use as a phase-shift photolithographicreticle. The silicon-based material of the substrate is prepared foretching by depositing and pattern etching a second resist material 250on the metal photomask layer and exposed portions of silicon-basedmaterial. The substrate is then transferred to a DPS™ processing chamberwhere a processing gas containing compounds adapted to etch thesilicon-based material is introduced into the processing chamber and aplasma is generated, thereby etching 260 the exposed silicon-basedmaterial of the substrate.

[0059] One example of etching of the silicon-based reticle of thesubstrate includes etching with a processing gas comprising fluorocarbongases as follows. The processing gas comprising fluorocarbon gaseshaving from 1 to 5 atoms of carbon and from 4 to 8 atoms of fluorineincluding CF₄, C₂F₆, C₄F₆, C₃F₈, C₄F₈, C₅F₈, and combinations thereof,is introduced into a processing chamber, such as the DPS™ describedabove, at a flow rate between about 25 sccm and about 100 sccm. Thechamber is maintained at a pressure between about 2 milliTorr and about50 milliTorr. An optional inert gas to enhance the etching process maybe introduced into the processing chamber at a flow rate between about30 sccm and about 150 sccm. A source RF power between about 50 watts andabout 200 watts is applied to an inductor coil to generate and sustainthe plasma during the process.

[0060] An optional bias power level between about 50 watts and about 200watts may be applied to the substrate support to enhance control of theetching process. During the etching process, the substrate is maintainedat a temperature between about 50° C. and about 150° C. Additionally,the sidewalls 15 of the processing chamber 10 are maintained at atemperature of less than about 70° C., and the dome is maintained at atemperature of less than about 80° C. to maintain consistent processingconditions and to minimize polymer formation on the surfaces of theprocessing chamber.

[0061] Etching of the silicon-based material of the substrate by theprocess described herein is more fully described in U.S. Pat. No.6,391,790, entitled “Method and Apparatus for Etching Photomasks,”issued on May 21, 2002, and incorporated herein by reference to theextent not inconsistent with aspects of the invention.

[0062] FIGS. 3A-3E illustrate the composition of the photolithographicreticle prior to the etching steps, as well as, further illustrating theprocess described above in FIG. 2. A substrate 300, typically made ofoptical quality quartz material 310, is introduced into a processingchamber. A metal layer 320 made of chromium is deposited on the quartzmaterial 310 as shown in FIG. 3A. The chromium layer may be deposited byconventional methods known in the art, such as by physical vapordeposition (PVD) or chemical vapor deposition (CVD) techniques. Thechromium layer 320 is typically deposited to a thickness between about50 and about 100 nanometers (nm) thick, however, the depth of the layermay change based upon the requirements of the manufacturer and thecomposition of the materials of the substrate or metal layer.

[0063] Referring to FIG. 3B, the substrate 300 is then transferred toanother processing chamber where a layer of resist material 330, such as“RISTON,” manufactured by DuPont de Nemours Chemical Company or othersimilar materials, is deposited upon the chromium layer 320 to athickness between about 200 and 600 nm thick. The resist material 330 isthen pattern etched using conventional laser or electron beam patterningequipment to form a first opening 325 which is used to define thedimensions of the second opening 335 to be formed in the chromium layer320.

[0064] The substrate 300 is then transferred to an etch chamber, such asthe DPS™ processing chamber 10 described above, and the chromium layer320 is etched using metal etching techniques known in the art or by newmetal etching techniques that may be developed to form the secondopening 335 which expose the underlying quartz material 310 as shown inFIG. 3C.

[0065] An exemplary processing regime for etching metal layers onsubstrates with the processing gas at the flow rates and bias describedherein are as follows. The substrate is placed on the support member 16,and a processing gas is introduced into the chamber and a plasma isgenerated to etch the chromium layer 320.

[0066] In one embodiment of the processing gas, the processing gascomprises oxygen gas, chlorine gas, and an inert gas. The processing gasis introduced into the processing chamber at a flow rate between about400 sccm and about 750 sccm. For example, a flow rate of about 460 sccmmay be used during the etching process. Oxygen gas is introduced intothe processing chamber at a flow rate between about 100 sccm and about400 sccm, for example about 120 sccm. Chlorine gas is introduced intothe processing chamber at a flow rate between about 200 sccm and about600 sccm, for example about 270 sccm. The inert gas, for example,helium, is introduced into the processing chamber at a flow rate betweenabout 0 sccm and about 500 sccm, for example about 70 sccm.

[0067] Generally, the processing chamber pressure is maintained betweenabout 15 milliTorr and about 32 milliTorr, for example about 20milliTorr. A source RF power between about 300 watts and about 1000watts, for example 650 watts, is applied to an inductor coil to generateand sustain a plasma of the processing gases during the etching process.A bias power between about 20 watts and about 40 watts, for exampleabout 30 watts, is applied to the substrate support.

[0068] The substrate temperature is between about 20° C. and about 100°C. during the etching process. Additionally, the sidewalls 15 of theprocessing chamber 10 are maintained at a temperature of about less thanabout 70° C. and the dome is maintained at a temperature of less thanabout 80° C. The above described metal etching process generallyproduces a selectivity of metal layer to resist of about 3:1 or greater.

[0069] Referring to FIGS. 3A-3C, after etching of the chromium layer 320is completed, the substrate 300 is transferred to a processing chamber.The remaining resist material 330 is usually removed from the substrate300, by an oxygen plasma process, or other resist removal techniqueknown in the art.

[0070] Referring to FIGS. 3D and 3E, the substrate 300 may be furtherprocessed to form a phase shift photolithographic reticle by etching thequartz material 310. In etching the quartz material 310, the resistmaterial 330 is removed and a second resist material 340 is applied andpatterned to expose the underlying quartz material 310 within the secondopening 335. The resist material is deposited to a depth between about200 nm and 600 nm thick, but may be of any thickness and may also be ofthe same thickness as the depth of the features to be etched in thequartz material 310 to form the photolithographic reticle. The substrate300 is then etched to form a third opening 345 in the resist layer 340,the metal layer 320, and the quartz material 310. The second resistmaterial 340 is removed to form a patterned substrate surface 355. Thepatterned substrate 300 is then transferred to an etch chamber, such asthe DPS™ processing chamber 10, for plasma etching of the quartzmaterial 310.

[0071] The above described processing gas composition and processingregime is believed to provide controllable etching of openings orpatterns with desired critical dimensions. The etching of the openingsor patterns is generally anisotropic. The anisotropic process removesmaterial deposited on the bottom of the opening at a higher rate thanmaterial on the sidewalls of the opening. This results in materials onthe sidewalls of the openings being removed at a lower rate thanmaterials on the bottoms of openings. The combination of the flow ratesand bias powers described herein improve the anisotropic etch of theplasma etching process, thereby increasing the etching rate of thebottom of the opening in contrast to the etching rate of the sidewallsof the opening. An etch process that etches the sidewalls of theopenings at a slower rate will be less likely to overetch the sidewallsallowing for improved preservation of the critical dimensions of theopenings being etched, and, thus, reducing etching bias.

[0072] It is believed that chromium layers deposited by physical vapordeposition techniques or chemical vapor deposition techniques mayincorporate contaminants, such as oxygen and nitrogen, during depositionor during substrate handling. Oxygen and nitrogen in the depositedchromium material form chromium oxynitride, which is mainly concentratedin the upper surface of the deposited material, such as the upper 30% ofthe chromium layer. The chromium oxynitride layer performs as anantireflective coating for the substrate and thus improves lithographicpatterning of the resist material. The chromium oxynitride film is moresensitive to etching with oxygen radicals than chromium films. A reducedamount of oxygen in the processing gas may be used to effectively etchthe chromium oxynitride surface compared to etching the bulk of theremaining chromium layer.

[0073] The invention is further described by the following examples thatare not intended to limit the scope of the claimed invention.

EXAMPLES

[0074] A photolithographic reticle including a substrate made of asilicon-based material, preferably optical quality quartz with achromium photomask layer approximately 100 nanometers (nm) thickdisposed thereon is introduced into a processing chamber for resistdeposition. A resist, such as ZEP, a resist material commerciallyavailable from Tokyo-Oka of Japan, or a chemically amplified resist orCAR resist also commercially available from Tokyo-Oka of Japan, isdeposited upon the chromium photomask and then patterned usingconventional laser or electron beam patterning equipment. The resistdeposited on the etched chromium photomask is between about 200 nm andabout 600 nm thick, for example, between about 300 nm and about 400 nmthick, but may be of any thickness desired.

Example 1

[0075] The reticle is placed in an etch chamber such as the DPS™ metaletch chamber described above. The patterned substrate also describedabove is placed on the cathode pedestal of the etch chamber, and thechamber is maintained at a pressure of about 20 milliTorr. A plasma wasgenerated by applying a source RF voltage to the inductor coil at apower level of about 650 watts. A bias power of 30 watts was applied tothe cathode pedestal. The substrate surface is maintained at atemperature between about 20° C. and about 50° C. The chamber walls anddome were cooled to less than about 70° C. to maintain a steady etchprocessing condition. The etching of the opening occurred under thefollowing gas flows: Oxygen (O₂), at 120 sccm Chlorine gas (Cl₂), at 270sccm Helium (He), at  70 sccm.

[0076] The total flow rate was about 460 sccm for the above listedprocessing gases. The etching process was performed for a sufficienttime to form the openings in the metal layer.

Example 2

[0077] The reticle is placed in an etch chamber such as the DPS™ metaletch chamber described above. The patterned substrate is placed on thecathode pedestal of the etch chamber, and the chamber is maintained at apressure of about 20 milliTorr. A plasma was generated by applying asource RF voltage to the inductor coil at a power level of about 650watts. A bias power of 30 watts was applied to the cathode pedestal. Thesubstrate surface is maintained at a temperature between about 20° C.and about 50° C. The chamber walls and dome were cooled to less thanabout 70° C. to maintain a steady etch processing condition. The etchingof the opening occurred under the following gas flows: Oxygen (O₂), at200 sccm Chlorine gas (Cl₂), at 300 sccm Helium (He), at  40 sccm.

[0078] The total flow rate was about 540 sccm for the above listedprocessing gases. The etching process was performed for a sufficienttime to form the openings in the metal layer.

Example 3

[0079] The reticle is placed in an etch chamber such as the DPS™ metaletch chamber described above. The patterned substrate is placed on thecathode pedestal of the etch chamber, and the chamber is maintained at apressure of about 20 milliTorr. A plasma was generated by applying asource RF voltage to the inductor coil at a power level of about 650watts. A bias power of 30 watts was applied to the cathode pedestal. Thesubstrate surface is maintained at a temperature between about 20° C.and about 50° C. The chamber walls and dome were cooled to less thanabout 70° C. to maintain a steady etch processing condition. The etchingof the opening occurred under the following gas flows: Oxygen (O₂), at360 sccm Chlorine gas (Cl₂), at 240 sccm Helium (He), at  0 sccm.

[0080] The total flow rate was about 600 sccm for the above listedprocessing gases. The etching process was performed for a sufficienttime to form the openings in the metal layer.

Example 4

[0081] The reticle is placed in an etch chamber such as the DPS™ metaletch chamber described above. The patterned substrate is placed on thecathode pedestal of the etch chamber, and the chamber is maintained at apressure of between about 20 milliTorr and about 30 milliTorr. A plasmawas generated by applying a source RF voltage to the inductor coil at apower level of about 650 watts. A bias power of 30 watts was applied tothe cathode pedestal. The substrate surface is maintained at atemperature between about 20° C. and about 50° C. The chamber walls anddome were cooled to less than about 70° C. to maintain a steady etchprocessing condition. The etching of the opening occurred under thefollowing gas flows: Oxygen (O₂), at  180 sccm Chlorine gas (Cl₂), at 480 sccm Helium (He), at 0-40 sccm.

[0082] The total flow rate was about 660-700 sccm for the above listedprocessing gases. The etching process was performed for a sufficienttime to form the openings in the metal layer.

[0083] While the foregoing is directed to the exemplary aspects of theinvention, other and further aspects of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for processing a photolithographicreticle, comprising: positioning the reticle on a support member in aprocessing chamber, wherein the reticle comprises a metal photomasklayer formed on a silicon-based substrate and a patterned resistmaterial deposited on the metal photomask layer; introducing aprocessing gas at a flow rate of at least 300 sccm, wherein theprocessing gas comprises an oxygen containing gas and a halogencontaining gas; delivering power to the processing chamber to generate aplasma of the processing gas; supplying a bias power to the supportmember of greater than about 5 watts; and removing exposed portions ofthe metal photomask layer.
 2. The method of claim 1, wherein the metalphotomask layer comprises chromium, chromium oxynitride, or combinationsthereof.
 3. The method of claim 1, wherein the silicon-based substratecomprises an optically transparent silicon-based material selected fromthe group of quartz, molybdenum silicide, molybdenum silicon oxynitride,and combinations thereof.
 4. The method of claim 1, wherein the oxygencontaining gas has a flow rate of at least 100 sccm.
 5. The method ofclaim 1, wherein the oxygen containing gas has a flow rate between about150 sccm and 400 sccm.
 6. The method of claim 1, wherein the oxygencontaining gas is selected from the group of oxygen, carbon monoxide,carbon dioxide, and combinations thereof.
 7. The method of claim 1,wherein the halogen containing gas has a flow rate of at least 200 sccm.8. The method of claim 1, wherein the halogen containing gas has a flowrate between about 200 sccm and 600 sccm.
 9. The method of claim 1,wherein the processing gas has a flow rate between about 350 sccm andabout 1000 sccm, wherein the oxygen containing gas has a flow ratebetween about 150 sccm and 400 sccm and the halogen containing gas has aflow rate between about 200 sccm and 600 sccm.
 10. The method of claim1, wherein the halogen containing gas and the oxygen containing gas havea molar ratio between about 1:1.5 and about 4:1.
 11. The method of claim1, wherein the halogen containing gas comprises a chlorine containinggas selected from the group of chlorine, carbon tetrachloride,hydrochloric acid, and combinations thereof.
 12. The method of claim 1,wherein the processing gas further comprises an inert gas selected fromthe group of helium, argon, xenon, neon, krypton, and combinationsthereof.
 13. The method of claim 1, wherein the inert gas has a flowrate of about 500 sccm or less.
 14. The method of claim 1, wherein thebias power is supplied at between about 20 watts and about 40 watts. 15.The method of claim 1, wherein the metal photomask layer and the resistmaterial are removed at a removal rate ratio of metal photomask layer toresist material between about 1:1 and about 3:1.
 16. The method of claim1, wherein processing the reticle comprises introducing the processinggas into a processing chamber, maintaining the processing chamber at apressure between about 2 milliTorr and about 50 milliTorr, maintainingthe reticle at a temperature between about 20° C. and about 150° C., andgenerating a plasma by supplying a source RF power between about 300watts and about 1000 watts to a coil in the processing chamber.
 17. Amethod for processing a photolithographic reticle, comprising:positioning the reticle on a support member in a processing chamber,wherein the reticle comprises a chromium-based photomask layer formed onan optically transparent silicon-based material and a patterned resistmaterial deposited on the chromium-based photomask layer; introducing aprocessing gas comprising chlorine gas and oxygen gas at a flow rate ofat least 350 sccm, wherein the molar ratio between the chlorine gas andthe oxygen gas is between about 1:1.5 and about 4:1; maintaining achamber pressure between about 2 milliTorr and about 50 milliTorr;delivering power to the processing chamber of about 1000 watts or lessto a coil disposed in the processing chamber to generate a plasma;supplying a bias power to the support member of greater than about 5watts; and etching exposed portions of the chromium-based photomasklayer; and removing the chromium-based photomask layer at a removal rateratio of chromium-based photomask layer to resist material of about 1:1or greater.
 18. The method of claim 17, wherein the chromium-basedphotomask layer comprises chromium, chromium oxynitride, or combinationsthereof, and the optically transparent silicon-based material comprisesquartz, molybdenum silicide, molybdenum silicon oxynitride, orcombinations thereof.
 19. The method of claim 17, further comprisingintroducing an inert gas selected from the group of helium, argon,xenon, neon, krypton, and combinations thereof.
 20. The method of claim17, wherein the processing gas has a flow rate between about 350 sccmand about 1000 sccm, wherein the oxygen gas has a flow rate betweenabout 150 sccm and 400 sccm and the chlorine gas has a flow rate betweenabout 200 sccm and 600 sccm.
 21. The method of claim 19, wherein theinert gas has a flow rate of about 500 sccm or less.
 22. The method ofclaim 17, wherein the bias power is supplied at between about 20 wattsand about 40 watts.
 23. The method of claim 17, wherein processing thereticle comprises introducing the processing gas into a processingchamber, maintaining the processing chamber at a pressure between about2 milliTorr and about 50 milliTorr, maintaining the reticle at atemperature between about 20° C. and about 150° C., and generating aplasma by supplying a source RF power between about 300 watts and about1000 watts to a coil to the processing chamber.
 24. The method of claim17, wherein the delivering power to the processing chamber to generate aplasma of the processing gas further comprises a plasma strike.
 25. Amethod for processing a photolithographic reticle, comprising:positioning the reticle on a support member in a processing chamber,wherein the reticle comprises a chromium-based photomask layer formed onan optically transparent silicon-based material and a patterned resistmaterial deposited on the chromium-based photomask layer; introducing afirst processing gas comprising an inert gas, a halogen containing gas,and an oxygen containing gas, wherein the halogen containing gas and theoxygen containing gas have a flow rate of about 100 sccm or less;delivering power to the processing chamber of about 1000 watts or lessto a coil disposed in the processing chamber to generate a plasma;introducing a second processing gas comprising a halogen containing gasand an oxygen containing gas, wherein the halogen containing gas and theoxygen containing gas have a flow rate of at least 350 sccm; deliveringpower to the processing chamber of about 1000 watts or less to a coildisposed in the processing chamber to maintain a plasma; supplying abias power to the support member of greater than about 5 watts; andetching exposed portions of the chromium-based photomask layer.
 26. Themethod of claim 26, wherein the second processing gas has an oxygencontaining gas flow rate between about 150 sccm and 400 sccm, whereinthe oxygen containing gas is selected from the group of oxygen, carbonmonoxide, carbon dioxide, and combinations thereof.
 27. The method ofclaim 26, wherein the second processing gas halogen containing gas flowrate is between about 200 sccm and 600 sccm, wherein the halogencontaining gas comprises a chlorine containing gas is selected from thegroup of chlorine, carbon tetrachloride, hydrochloric acid, andcombinations thereof.
 28. The method of claim 26, wherein the secondprocessing gas has a flow rate between about 350 sccm and about 1000sccm, wherein the oxygen containing gas has a flow rate between about150 sccm and 400 sccm and the halogen containing gas has a flow ratebetween about 200 sccm and 600 sccm.
 29. The method of claim 26, whereinthe second processing gas has a molar ratio of the halogen containinggas to the oxygen containing between about 1:1.5 and about 4:1.
 30. Themethod of claim 26, wherein the second processing gas further comprisesan inert gas selected from the group of helium, argon, xenon, neon,krypton, and combinations thereof.
 31. The method of claim 26, whereinthe plasma is maintained by a process comprising maintaining theprocessing chamber at a pressure between about 2 milliTorr and about 50milliTorr, maintaining the reticle at a temperature between about 50° C.and about 150° C., generating a plasma by supplying a source RF powerbetween about 300 watts and about 1000 watts to a coil in the processingchamber, and supplying the bias power at between about 20 watts andabout 40 watts.